Diversity ofβ-Lactamase Activity among Clinical Isolates of Gram-negative Bacilli

Various properties (specific activity, inducibility, substrate profile, and susceptibility to inhibitors) of the beta-lactamase activity present in 39 strains of Enterobacteriaceae and Pseudomonas aeruginosa isolated during a two-month period in the bacteriology laboratory of a large general hospital were investigated. Among the 39 strains there appeared to be at least 16 distinct enzymes. Most enzymes from Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, and Proteus morganii were active against both penicillins and cephalosporins, whereas those from Proteus vulgaris, Serratia marcescens and Pseudomonas aeruginosa showed activity primarily against cephalosporins. Both types of enzyme were found among strains of Enterobacter. There was a general correlation between amount of enzymic activity and levels of resistance to several beta-lactam antibiotics. Discrepancies between enzymic activity and resistance to several beta-lactam antibiotics. Discrepancies between enzymic activity and resistance may be due to variations in the roles intrinsic mechanisms play in resistance to various antibiotics.